Image sensing apparatus and method using radiation

ABSTRACT

This invention is to provide a radiation image sensing apparatus capable of automatically adjusting an incident radiation dose without requiring high-speed driving while suppressing any attenuation of the radiation before detection, and a method of manufacturing the same. To accomplish this, a read TFT ( 1 ) is formed on an insulating substrate ( 11 ). The semiconductor layer ( 19 ) and n + -semiconductor layer ( 20 ) of an MIS photoelectric conversion element ( 2 ) are formed on a second insulating layer ( 18 ) that covers the read TFT ( 1 ) to be aligned with source and drain electrodes ( 16 ) functioning as lower electrodes. The semiconductor layer ( 21 ) of a TFT sensor ( 3 ) is formed to be aligned with a gate electrode ( 17 ) when viewed from the upper side. The semiconductor layers ( 19, 21 ) are formed from the same layer. The upper electrode ( 22 ) of the MIS photoelectric conversion element ( 2 ) is formed on the n + -semiconductor layer ( 20 ). Two ohmic contact layers ( 23 ) are formed on the semiconductor layer ( 21 ). Source and drain electrodes ( 24 ) are formed on the two ohmic contact layers ( 23 ), respectively.

This application is a continuation of application Ser. No. 10/648,916,which was filed on Aug. 27, 2003 and which is hereby incorporated byreference in its entirety herein. This application claims the benefit offoreign priority based on Japanese Patent Application No. 2002-247249,filed on Aug. 27, 2002, and 2003-017806, filed on Jun. 30, 2003, each ofwhich is hereby incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to a radiation image sensing apparatussuitable for a medical image diagnostic apparatus, a nondestructiveinspection apparatus, and an analyzing apparatus using radiation and amethod of manufacturing the radiation image sensing apparatus.

BACKGROUND OF THE INVENTION

A typical radiation image sensing apparatus that has conventionally beenused is an apparatus that combines a photosensor having a MIS-TFTstructure constructed by a MIS photoelectric conversion element and aswitching TFT and a phosphor to convert radiation into visible light. Inthis specification, radiation includes not only α-rays, β-rays, andγ-rays but also electromagnetic waves such as visible light and X-rays.

FIG. 9 is an equivalent circuit diagram showing the circuit arrangementof a conventional radiation image sensing apparatus. FIG. 10 is a planview showing the layout structure in the conventional radiation imagesensing apparatus.

As an example of a radiation image sensing apparatus, one photoelectricconversion element (semiconductor conversion element) and one thin filmtransistor (TFT) are arranged for each pixel. More specifically, a pixelon the ath row and bth column from the upper side in FIGS. 9 and 10 hasone photoelectric conversion element Mba and one thin film transistorTba (a, b=1, 2, 3, 4).

Four photoelectric conversion elements arranged on the bth column areconnected to a common bias line Vsb so that a predetermined bias isapplied from a reading unit. The gate electrodes of four TFTs arrangedon the ath row are connected to a common gate line Vga so that the gatesare ON/OFF-controlled by a gate driving unit. The source electrodes ordrain electrodes of the four TFTs arranged on the bth column areconnected to a common signal line Sigb. Signal lines Sig1 to Sig4 areconnected to the reading unit.

A phosphor layer that converts X-rays into visible light is formed onthe irradiation surface of the radiation image sensing apparatus.

X-rays that irradiate an object such as a human body to be inspected onthe radiation image sensing apparatus pass through the object to beinspected while being attenuated by it. The X-rays are converted intovisible light by the phosphor layer. The visible light strikes thephotoelectric conversion element and is converted into charges. Thecharges are transferred to a signal line through TFTs in accordance witha gate driving pulse applied from the gate driving unit and output tothe outside through the reading unit. After that, charges that aregenerated by the photoelectric conversion element and remain therewithout being transferred are removed through the common bias line. Thisoperation is called “refresh”.

FIG. 11 is a sectional view showing the layer structure of one pixel ofa photosensor having a conventional MIS-TFT structure. FIG. 11 shows aphotosensor in which a MIS photoelectric conversion element and aswitching TFT are formed in parallel.

An MIS photoelectric conversion element 1001 and switching TFT 1002 areformed on an insulating substrate 1011. The MIS photoelectric conversionelement 1001 has a lower electrode 1017, insulating layer 1018,semiconductor layer 1019, n⁺-semiconductor layer 1020, and upperelectrode 1022. The switching TFT 1002 has a gate electrode 1012 gateinsulating layer 1013, semiconductor layer 1014, ohmic contact layer1015, and two, source and drain electrodes 1016.

The lower electrode 1017 and gate electrode 1012 are formed from thesame electrode layer. The insulating layer 1018 and gate insulatinglayer 1013 are formed from the same insulating layer. The semiconductorlayer 1019 and semiconductor layer 1014 are formed from the samesemiconductor layer. The upper electrode 1022 and source and drainelectrodes 1016 are formed from the same electrode layer.

The lower electrode 1017 of the MIS photoelectric conversion element1001 is connected to one of the source and drain electrodes 1016 of theswitching TFT 1002. The upper electrode 1022 is connected to a biasline. The other of the source and drain electrodes 1016 is connected toa signal line. The gate electrode 1012 is connected to a gate line. Aninsulating layer (protective layer) 1025, organic protective layer 1026,adhesive layer 1027, and phosphor layer 1028 are formed on the elements.

An X-ray automatic exposure controller (AEC) which automaticallycontrols exposure of X-rays emitted from an X-ray source in theradiation image sensing apparatus will be described next.

Generally, in a radiation image sensing apparatus havingtwo-dimensionally arrayed sensors, the dose of incident X-rays must beadjusted (AEC-controlled) for each object to be inspected or everyimaging. X-ray dose adjustment methods can be classified into twomethods.

(1) An AEC sensor is arranged independently of the radiation imagesensing apparatus.

(2) An X-ray dose is read out from all or some of the image sensors inthe radiation image sensing apparatus at a high speed, and the readsignal is used as an AEC signal.

Conventionally, when the method (1) is employed, a plurality of thin AECsensors which attenuate X-rays by about 5% are separately arranged infront of the radiation image sensing apparatus, i.e., on the detectedobject side of the phosphor layer of the radiation image sensingapparatus. X-ray exposure is stopped on the basis of the outputs fromthese AEC sensors, thereby obtaining an appropriate X-ray dose forimaging. As an AEC sensor used in this method, a sensor which directlyextracts X-rays as charges by using an ion chamber, or a sensor whichextracts phosphor light through a phosphor by using a fiber and causes aphotomultiplier to convert the light into charges is used.

However, when AEC sensors are separately prepared in the radiation imagesensing apparatus in which sensors are two-dimensionally arrayed toadjust (AEC-control) an incident radiation dose, the layout of thesensors poses a problem.

Generally, information necessary for AEC is present at the center of anobject. If AEC sensors should be laid out without impeding image sensingby image sensing sensors, AEC sensors that attenuate radiation by only aminimum amount must be independently arranged, resulting in an increasein cost of the entire apparatus. In addition, there are no sensors thatdo not attenuate radiation at all. Hence, the quality of a sensed imageinevitably degrades.

The method that uses image sensing sensors in the radiation imagesensing apparatus as AEC sensors poses no serious problem for sensorswith a relatively small number of pixels. However, when the number ofpixels is, e.g., 2,000×2,000, a high-speed driving circuit is necessary,resulting in an increase in cost of the entire apparatus. Sincehigh-speed driving is necessary, it is difficult to sufficiently ensurethe charge storage time, charge transfer time, and capacitor reset timein the image sensing sensors. As a result, the quality of a sensed imagedegrades.

Contrary to this arrangement, U.S. Pat. No. 5,448,613 discloses anarrangement in which a second pixel group is arranged in a sensorsubstrate and driven by a shift register different from that for animage read sensor to detect the integration of signal charges.

However, when this arrangement is simply employed, some of image readpixels are replaced with second pixels. Accordingly, the opening ratioof pixels related to image reading with respect to all the pixelsdecreases. In addition, lead interconnections must be preparedseparately for the first pixels and second pixels. This may complicatethe interconnection structure.

Hence, there is still room for improvement in the arrangement of theabove prior art in association with the pixel layout and interconnectionstructure.

SUMMARY OF THE INVENTION

Accordingly, the present invention is conceived as a response to theabove-described disadvantages of the conventional art.

According to one aspect of the present invention, preferably, an imagesensing apparatus is characterized by comprising a substrate, aconversion section which is arranged on the substrate and has a firstsemiconductor conversion element that converts radiation into anelectrical signal and a switch element connected to the firstsemiconductor conversion element, and a second semiconductor conversionelement which is arranged on the substrate to detect a total dose ofradiation incident on the conversion section and converts the radiationinto an electrical signal, wherein the first semiconductor conversionelement and the second semiconductor conversion element havesemiconductor layers formed from the same layer.

According to the other aspect of the present invention, preferably, aradiation image sensing apparatus is characterized by comprising asubstrate, a conversion section which is arranged on the substrate andhas a first photoconductive element, a capacitive element connected tothe first photoconductive element, and a switch element connected to thecapacitive element, and a second photoconductive element which isarranged on the substrate to detect a total dose of radiation incidenton the conversion section, wherein the first photoconductive element andthe second photoconductive element have photoconductive layers formedfrom the same layer.

According to still other aspect of the present invention, preferably, amethod of manufacturing a radiation image sensing apparatus having asubstrate, a conversion section which is arranged on the substrate andhas a first semiconductor conversion element that converts radiationinto an electrical signal and a switch element connected to the firstsemiconductor conversion element, and a second semiconductor conversionelement which is arranged on the substrate to detect a total dose ofradiation incident on the conversion section and converts the radiationinto an electrical signal is characterized by comprising steps offorming the switch element on the substrate, and forming a semiconductorlayer of the first semiconductor conversion element and a semiconductorlayer of the second semiconductor conversion element simultaneously fromthe same layer.

According to still other aspect of the present invention, preferably, amethod of manufacturing a radiation image sensing apparatus having asubstrate, a conversion section which is arranged on the substrate andhas a first photoconductive element, a capacitive element connected tothe first photoconductive element, and a switch element connected to thecapacitive element, and a second photoconductive element which isarranged on the substrate to detect a total dose of radiation incidenton the conversion section is characterized by comprising steps offorming the switch element and the switch on the substrate, and forminga photoconductive layer of the first photoconductive element and aphotoconductive layer of the second photoconductive element from thesame layer.

In the present invention, AEC can be executed on the basis of aradiation dose detected through the second semiconductor conversionelement or second photoconductive element. The second semiconductorconversion element or second photoconductive element is formed on thesame substrate as that of the first semiconductor conversion element orfirst photoconductive element. Hence, radiation is not attenuated by thesecond semiconductor conversion element or second photoconductiveelement. In addition, since the first semiconductor conversion elementor first photoconductive element need not be used for automatic control,the element need not be driven at a high speed.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures there.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit diagram showing the circuit arrangementof a radiation image sensing apparatus according to the first embodimentof the present invention;

FIG. 2 is a plan view showing the layout structure of the radiationimage sensing apparatus according to the first embodiment of the presentinvention;

FIG. 3 is a sectional view showing the layer structure of one pixel ofthe radiation image sensing apparatus according to the first embodimentof the present invention;

FIG. 4 is an equivalent circuit diagram showing the circuit arrangementof a radiation image sensing apparatus according to the secondembodiment of the present invention;

FIG. 5 is a plan view showing the layout structure of the radiationimage sensing apparatus according to the second embodiment of thepresent invention;

FIG. 6 is a sectional view showing the layer structure of one pixel ofthe radiation image sensing apparatus according to the second embodimentof the present invention;

FIG. 7 is a sectional view showing the layer structure of one pixel of aradiation image sensing apparatus according to the third embodiment ofthe present invention;

FIG. 8 is a sectional view showing the layer structure of one pixel ofthe radiation image sensing apparatus according to the fourth embodimentof the present invention;

FIG. 9 is an equivalent circuit diagram showing the circuit arrangementof a conventional radiation image sensing apparatus;

FIG. 10 is a plan view showing the layout structure of the conventionalradiation image sensing apparatus shown in FIG. 9;

FIG. 11 is a sectional view showing the layer structure of one pixel ofa photosensor having a conventional MIS-TFT structure;

FIG. 12 is an equivalent circuit diagram showing the circuit arrangementof a radiation image sensing apparatus according to a reference example;

FIG. 13 is a layout diagram showing the overall arrangement of theradiation image sensing apparatus according to the reference example;

FIG. 14 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the referenceexample, which has neither a monitor photoelectric conversion elementnor lead interconnections therefor;

FIG. 15 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the referenceexample, which has a monitor photoelectric conversion element;

FIG. 16 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the referenceexample, which has lead interconnections for a monitor photoelectricconversion element;

FIG. 17 is a sectional view taken along a line I-I in FIG. 14;

FIG. 18 is a layout diagram showing the planar structure of a pixel of aradiation image sensing apparatus according to the fifth embodiment ofthe present invention, which has a monitor photoelectric conversionelement;

FIG. 19 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the fifth embodiment,which has lead interconnections for a monitor photoelectric conversionelement;

FIG. 20 is a sectional view taken along a line II-II in FIG. 18;

FIG. 21 is a schematic view showing the layout of a conversion section Tand circuit sections around it;

FIGS. 22A to 22D are sectional views showing steps in manufacturing theradiation image sensing apparatus according to the fifth embodiment ofthe present invention;

FIGS. 23A to 23C are sectional views showing steps in manufacturing theradiation image sensing apparatus according to the fifth embodiment ofthe present invention, which show the steps next to those shown in FIGS.22A to 22D;

FIG. 24 is a layout diagram showing the overall arrangement of aradiation image sensing apparatus according to the sixth embodiment ofthe present invention;

FIG. 25 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the sixth embodiment,which has a monitor photoelectric conversion element;

FIG. 26 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the sixth embodiment,which has lead interconnections for a monitor photoelectric conversionelement;

FIG. 27 is a sectional view taken along a line III-III in FIG. 25;

FIGS. 28A to 28D are sectional views showing a method of manufacturingthe radiation image sensing apparatus according to the sixth embodimentof the present invention; and

FIGS. 29A to 29D are sectional views showing the method of manufacturingthe radiation image sensing apparatus according to the sixth embodimentof the present invention, which show the steps next to those shown inFIGS. 28A to 28D.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. It should be noted that therelative arrangement of the components, the numerical expressions andnumerical values set forth in these embodiments do not limit the scopeof the present invention unless it is specifically stated otherwise.

The embodiments of the present invention will be described below indetail with reference to the accompanying drawings. A reference examplewill be described for the sake of understanding of the presentinvention. This reference example is based on the description of U.S.Pat. No. 5,448,613 described above. FIG. 12 is an equivalent circuitdiagram showing the circuit arrangement of a radiation image sensingapparatus according to the reference example. FIG. 13 is a layoutdiagram showing the overall arrangement of the radiation image sensingapparatus according to the reference example. FIG. 12 shows an examplein which 4 (rows)×4 (columns) (=a total of 16) pixels are arranged in apixel area. However, the number of pixels is not limited to this.

In this reference example, a combination of an image sensingphotoelectric conversion element (first photoelectric conversionelement) and a switching thin film transistor (TFT) or a combination ofan image sensing photoelectric conversion element, switching TFT, andmonitor photoelectric conversion element (second photoelectricconversion element) for AEC is arranged for each pixel. Morespecifically, a pixel on the ath row and the bth column from the upperside in FIG. 12 has one image sensing photoelectric conversion elementMba and one switching thin film transistor Tba (a, b=1, 2, 3, 4). Thepixels on the fourth column and the third and fourth rows respectivelyhave monitor photoelectric conversion elements MA33 and MA34. The pixelson the fourth column and the first and second rows respectively havelead interconnections for the monitor photoelectric conversion elements.

The four image sensing photoelectric conversion elements arranged on thebth column are connected to a common bias line Vsb so that apredetermined bias is applied from a common electrode driver circuit156. The gate electrodes (control electrodes) of the four switching TFTsarranged on the ath row are connected to a common gate line Vga so thatthe gates are ON/OFF-controlled by a gate driver circuit 152. The sourceelectrodes or drain electrodes of the four switching TFTs arranged onthe bth column are connected to a common signal line Sigb. Signal linesSig1 to Sig4 are connected to an image sensing signal processing circuit151. Arrays of pixels arranged in the direction in which the bias linesrun will be referred to as “columns”. Arrays of pixels arranged in adirection (the direction in which gate lines run) perpendicular to thecolumns will be referred to as “rows”.

The monitor photoelectric conversion elements MA33 and MA34 are TFTsensors. Their source electrodes are connected to a power supply 153,their drain electrodes are connected to a monitor signal processingcircuit 154, and their gate electrodes (control electrodes) areconnected to the gate driver circuit 152. In a TFT sensor, electrons andholes generated in a semiconductor layer when visible light becomesincident on it are read in accordance with an electric field between thesource and the drain. That is, when a voltage is applied from the powersupply 153 to each source electrode to apply a potential between thesource and the drain, electrons and holes generated when thelight-receiving portion between the electrodes is irradiated with lightare transported to each electrode by the potential difference betweenthe source and the drain. When the charges are read in real time by themonitor signal processing circuit 154, the light irradiation amount canbe measured.

When a circuit having the arrangement shown in FIG. 12 is applied to aradiation image sensing apparatus having a number of pixels, aconversion section (pixel area) T includes an area R1 where a pluralityof pixels each having an image sensing photoelectric conversion elementand switching TFT are collectively laid out, areas R2 where a pluralityof pixels each having an image sensing photoelectric conversion element,switching TFT, and monitor photoelectric conversion element arecollectively laid out, and areas R3 where a plurality of pixels eachhaving an image sensing photoelectric conversion element, switching TFT,and lead interconnection for a monitor photoelectric conversion elementare collectively laid out, as shown in FIG. 13.

The planar structure of each of the three types of pixels in thereference example will be described next. FIG. 14 is a layout diagramshowing the planar structure of a pixel of the radiation image sensingapparatus according to the reference example, which has neither amonitor photoelectric conversion element nor lead interconnectionstherefor. FIG. 15 is a layout diagram showing the planar structure of apixel of the radiation image sensing apparatus according to thereference example, which has a monitor photoelectric conversion element.FIG. 16 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to the referenceexample, which has lead interconnections for a monitor photoelectricconversion element. FIG. 17 is a sectional view taken along a line I-Iin FIG. 14. Referring to FIGS. 14 to 16, a semiconductor layer isillustrated inside a control electrode that is present under thesemiconductor layer for the illustrative convenience. In this referenceexample, the semiconductor layer or photoelectric conversion layer isformed to be wider than the control electrode that is present under thesemiconductor layer or photoelectric conversion layer, and a firstinsulating film is present under the semiconductor layer orphotoelectric conversion layer, as shown in FIGS. 14 and 17. This alsoapplies to the remaining layout diagrams.

In the pixel which has neither a monitor photoelectric conversionelement nor lead interconnections therefor, a sensor electrode 111 of animage sensing photoelectric conversion element 101, a control electrode(gate electrode) 112 of a switching TFT 103, and a first insulating film113 that covers the sensor electrode 111 and control electrode 112 areformed on an insulating substrate 110, as shown in FIGS. 14 and 17.

On the first insulating film 113, a semiconductor layer (photoelectricconversion layer) 114 a and ohmic contact layer 115 a are sequentiallystacked to be aligned with the sensor electrode 111. A common electrodebias line 116 is formed on the ohmic contact layer 115 a. The commonelectrode bias line 116 corresponds to bias lines Vs1 to Vs4 in FIG. 12.

Also, a semiconductor layer 114 b is formed on the first insulating film113 to be aligned with the control electrode 112. Ohmic contact layers115 b are formed at two portions on the semiconductor layer 114 b. Oneohmic contact layer 115 b extends to a portion on the sensor electrode111. A drain electrode 117 d is formed on the ohmic contact layer 115 bthat extends to a portion on the sensor electrode 111. A sourceelectrode 117 s is formed on the other ohmic contact layer 115 b. Athrough hole 127 is formed through one ohmic contact layer 115 b, thesemiconductor layer 114 b, and the first insulating film 113. The drainelectrode 117 d is electrically connected to the sensor electrode 111.

A second insulating film 118 is formed to cover the resultant structure.A phosphor layer (not shown) which converts X-rays into visible light isformed on the second insulating film 118.

The source electrode 117 s is connected to a signal line 119. Thecontrol electrode 112 is connected to a gate line 120. The signal line119 corresponds to the signal lines Sig1 to Sig4 in FIG. 12. The gateline 120 corresponds to gate lines Vg1 to Vg4 in FIG. 12. A pixel havingthe structure shown in FIG. 14 is present at least in the area R1. Thepixel may be present in the areas R2 and R3.

The structure of a pixel having a monitor photoelectric conversionelement will be described next. In this pixel, a control electrode 121of a monitor photoelectric conversion element 102 is formed on theinsulating substrate 110 in addition to the sensor electrode 111 of theimage sensing photoelectric conversion element 101 and the controlelectrode (gate electrode) 112 of the switching TFT 103, as shown inFIG. 15. The electrodes are covered with the first insulating film 113.This pixel will be compared with that shown in FIGS. 14 and 17. Theshapes and areas of the pixels are the same. In the pixel shown in FIG.15, since the control electrode 121 is formed, the sensor electrode 111and the like are smaller. The structures of the image sensingphotoelectric conversion element 101 and switching TFT 103 are the sameas those of the pixel shown in FIGS. 14 and 17 except that the imagesensing photoelectric conversion element 101 is smaller.

In the monitor photoelectric conversion element 102, a semiconductorlayer (photoelectric conversion layer) 114 c is formed on the firstinsulating film 113 to be aligned with the control electrode 121. Ohmiccontact layers (second electrodes) 115 c are formed at two portions onthe semiconductor layer 114 c. A drain electrode 122 d and a sourceelectrode 122 s are formed on the two ohmic contact layers 115 c,respectively. The drain electrode 122 d and source electrode 122 s arecovered with the second insulating film 118.

As shown in FIG. 15, the control electrode 121 is formed to be longerthan the semiconductor layer 114 c. A through hole 128 is formed at aposition of the first insulating film 113, which is aligned to the twoterminal portions of the control electrode 121. An upper interconnection123 which electrically connects the control electrodes 121 of pixelsthat are adjacent to each other via the gate line 120 is formed over thegate line 120 through the through hole 128. A pixel having the structureshown in FIG. 15 is present in the area R2.

A pixel having lead interconnections for a monitor photoelectricconversion element has an interconnection 124 for the drain electrode122 d, an interconnection 125 for the control electrode 121, and aninterconnection 126 for the source electrode 122 s, as shown in FIG. 16.The interconnections 124 to 126 run in parallel to the common electrodebias line 116. The interconnections are laid out to be adjacent to theimage sensing photoelectric conversion element 101 in the pixel alongthe direction in which the gate interconnection 120 runs. This pixelwill be compared with that shown in FIGS. 14 and 17. The shapes andareas of the pixels are the same. In the pixel shown in FIG. 16, sincethe interconnections 124 to 126 are formed, the sensor electrode 111 andthe like are smaller. The structures of the image sensing photoelectricconversion element 101 and switching TFT 103 are the same as those ofthe pixel shown in FIGS. 14 and 17 except that the image sensingphotoelectric conversion element 101 is smaller. A pixel having thestructure shown in FIG. 16 is present in the area R3.

Although not illustrated in FIG. 17, a phosphor layer which convertsX-rays into visible light is formed on the second insulating film 118.

According to the reference example having the above arrangement, sincethe monitor photoelectric conversion element 102 is formed on theinsulating substrate 110 independently of the image sensingphotoelectric conversion element 101, any separate radiation monitorboard need not be prepared, and the entire apparatus can be made compactand lightweight.

However, as shown in FIG. 15, the through hole 128 must be formed toconnect the control electrode 121 and upper interconnection 123. Hence,the light-receiving area of the image sensing photoelectric conversionelement 101 is not sufficiently large. In addition, as shown in FIG. 16,in the pixel having the lead interconnections 124 to 126, thelight-receiving area of the image sensing photoelectric conversionelement 101 is much smaller than that of the pixel shown in FIG. 14. Forthe arrangement of this reference example, the opening ratios of the twophotoelectric conversion elements 101 and 102 must be further increased.

A radiation image sensing apparatus according to each embodiment of thepresent invention and a method of manufacturing the apparatus will bedescribed below in detail with reference to the accompanying drawings.

First Embodiment

The first embodiment of the present invention will be described first.FIG. 1 is an equivalent circuit diagram showing the circuit arrangementof a radiation image sensing apparatus according to the first embodimentof the present invention. FIG. 2 is a plan view showing the layoutstructure of the radiation image sensing apparatus according to thefirst embodiment. FIG. 3 is a sectional view showing the layer structureof one pixel of the radiation image sensing apparatus according to thefirst embodiment. FIGS. 1 and 2 show an example in which 4 (rows)×4(columns) (=a total of 16) pixels are arranged in a pixel area. However,the number of pixels is not limited to this. For example, 2,000×2,000pixels may be arranged. Semiconductor conversion elements here includean optical conversion element which converts light into charges and aradiation conversion element which directly converts radiation intocharges.

In this embodiment, a combination of a MIS photoelectric conversionelement (first semiconductor conversion element) and a read thin filmtransistor (TFT) (switch element) or a combination of a MISphotoelectric conversion element (first semiconductor conversionelement), read TFT (switch element), and TFT sensor (secondsemiconductor conversion element) for AEC is arranged for each pixel.More specifically, a pixel on the ath row and the bth column from theupper side in FIGS. 1 and 2 has one photoelectric conversion element Mbaand one thin film transistor Tba (a, b=1, 2, 3, 4). A pixel on the athrow and the third column also has one TFT sensor MA3 a.

Four MIS photoelectric conversion elements arranged on the bth columnare connected to a common bias line Vsb so that a predetermined bias isapplied from a reading unit. The gate electrodes of four read TFTsarranged on the ath row are connected to a common gate line Vga so thatthe gates are ON/OFF-controlled by a gate driving unit. The sourceelectrodes or drain electrodes of the four read TFTs arranged on the bthcolumn are connected to a common signal line Sigb. Signal lines Sig1 toSig4 are connected to the reading unit.

The layer structure of the pixel having the TFT sensor will be describedhere with reference to FIG. 3. This pixel has a channel-etching-typeread TFT 1, MIS photoelectric conversion element 2, and TFT sensor 3.

As the layer structure of this pixel, a gate electrode 12 for the readTFT 1 and a first insulating layer 13 which covers the gate electrode 12are formed on an insulating substrate 11. The first insulating layer 13functions as the gate insulating film of the read TFT 1.

A semiconductor layer (channel layer) 14 of the read TFT 1 is formed onthe first insulating layer 13. Ohmic contact layers 15 are formed on thesemiconductor layer 14. Source and drain electrodes 16 are formed on theohmic contact layers 15, respectively. One of the source and drainelectrodes 16 is formed to extend from the ohmic contact layer 15 to thefirst insulating layer 13. The source and drain electrodes 16 alsofunction as the lower electrodes of the MIS photoelectric conversionelement 2. A gate electrode 17 of the TFT sensor 3 is also formed on thefirst insulating layer 13. A second insulating layer 18 that covers thegate electrode 17 and source and drain electrodes 16 is formed. Thesecond insulating layer 18 functions as the gate insulating film of theTFT sensor 3.

A semiconductor layer 19 and an n⁺-semiconductor layer 20 are formed onthe second insulating layer 18 to be aligned with the source and drainelectrodes 16 that also function as the lower electrode of the MISphotoelectric conversion element 2 when viewed from the upper side. Asemiconductor layer (channel layer) 21 of the TFT sensor 3 is alsoformed on the second insulating layer 18. The semiconductor layers 19and 21 are formed from the same layer, as will be described later. Anupper electrode 22 of the MIS photoelectric conversion element 2 isformed on the n⁺-semiconductor layer 20. The n⁺-semiconductor layer 20functions as an upper electrode. Ohmic contact layers (n⁺-semiconductorlayers) 23 are formed on the semiconductor layer 21. Source and drainelectrodes 24 are formed on the ohmic contact layers 23, respectively. Athird insulating layer 25 that covers the upper electrode 22 and sourceand drain electrodes 24 is formed.

An organic protective layer 26, adhesive layer 27, and phosphor layer 28are sequentially formed on the third insulating layer 25.

As the read TFT 1, a TFT with a high transfer speed is preferably used.Hence, the semiconductor layer 14 is a thin film. On the other hand, theMIS photoelectric conversion element 2 and TFT sensor 3 can preferablyabsorb incident light sufficiently. Hence, the semiconductor layers 19and 21 are preferably thicker than the semiconductor layer 14. The speedmay be further increased by using a TFT made of polysilicon as the readTFT 1.

In the layer structure of a pixel that has no TFT sensor 3, the gateelectrode 17, semiconductor layer 21, ohmic contact layers 23, andsource and drain electrodes 24 are omitted from the structure shown inFIG. 3.

The upper electrode 22 of the MIS photoelectric conversion element 2 isconnected to a bias line. One of the source and drain electrodes 16,which is not used as the lower electrode, is connected to a signal line.The gate electrode 12 is connected to a gate line. In the TFT sensor 3,the gate electrode 17 and source and drain electrodes 24 are connectedto a reading unit.

The operation of the radiation image sensing apparatus according to thefirst embodiment having the above arrangement will be described next.

When an object such as a human body to be inspected is exposed to X-rayson this radiation image sensing apparatus, the X-rays pass through theobject to be inspected while being attenuated by it. The X-rays areconverted into visible light by the phosphor layer 28. The visible lightstrikes the MIS photoelectric conversion element 2 and is converted intocharges. The charges are transferred to the signal line through the readTFT 1 in accordance with a gate driving pulse applied from a gatedriving unit and output to the outside through the reading unit. Afterthat, charges that are generated by the MIS photoelectric conversionelement 2 and remain there without being transferred are removed throughthe common bias line.

For the TFT sensor 3, for example, a predetermined bias that depletesthe semiconductor layer 21 is applied between the source and drainelectrodes 24 in advance. When a predetermined bias is applied inadvance, charges corresponding to incident light are always output. Whenthe output value is amplified by an amplifier (AMP) and added, the totalX-ray dose can be detected by the reading unit. X-ray exposure iscontrolled on the basis of the total X-ray dose.

According to the first embodiment, the AEC sensor is formed on theinsulating substrate independently of the image sensing sensor. For thisreason, the total X-ray dose can be sufficiently detected withoutdriving the image sensing sensor (MIS photoelectric conversion element2) at a high speed. In addition, since the MIS photoelectric conversionelement 2 need not be driven at a high speed, the charge storage time,charge transfer time, and capacitor reset time can be sufficientlyensured. Hence, an image with a high image quality can be sensed.

In addition, X-rays are not attenuated by the AEC sensor beforeincidence on the MIS photoelectric conversion element 2. Hence, a highimage quality can be obtained.

The TFT sensor 3 can be selectively laid out at a necessary position.That is, not all the TFT sensors 3 need be laid out on one column ofpixels, unlike FIG. 1. In a pixel having the TFT sensor 3, the openingratio of the MIS photoelectric conversion element 2 decreases. However,the decrease in area can easily be compensated by image correction afterthe read.

A method of manufacturing the radiation image sensing apparatusaccording to the first embodiment will be described next.

First, a first electrode layer is formed on the insulating substrate 11and patterned to form the gate electrode 12. Next, the first insulatinglayer 13 is formed on the entire surface.

A first semiconductor layer is formed on the first insulating layer 13and patterned to form the semiconductor layer 14. The ohmic contactlayers 15 are formed on the semiconductor layer 14. Subsequently, asecond electrode layer is formed on the entire surface and patterned toform the source and drain electrodes 16 and gate electrode 17. Thesecond insulating layer 18 is formed on the entire surface.

A second semiconductor layer is formed on the entire surface andpatterned to form the semiconductor layers 19 and 21 simultaneously.After that, the n⁺-semiconductor layer 20 is formed on the semiconductorlayer 19, and the ohmic contact layers 23 are formed on thesemiconductor layer 21. A third electrode layer is formed on the entiresurface and patterned to form the upper electrode 22 and source anddrain electrodes 24. The third insulating layer 25 is formed on theentire surface.

After that, the organic protective layer 26, adhesive layer 27, andphosphor layer 28 are sequentially formed on the entire surface. In thepresent invention, when a transparent electrode layer made of ITO(Indium Tin Oxide) or the like is formed between the third insulatinglayer 25 and the n⁺-semiconductor layer 20 or ohmic contact layers 23,the n⁺-semiconductor layer 20 can be made thin. Accordingly, theincident light amount itself can be increased. Even in the TFT sensor 3,when a transparent electrode layer is used for the source and drainelectrodes 24, the incident light amount can be increased. Hence, thesensitivity of the TFT sensor increases.

In this way, the radiation image sensing apparatus according to thefirst embodiment can be manufactured.

Second Embodiment

The second embodiment of the present invention will be described next.FIG. 4 is an equivalent circuit diagram showing the circuit arrangementof a radiation image sensing apparatus according to the secondembodiment of the present invention. FIG. 5 is a plan view showing thelayout structure of the radiation image sensing apparatus according tothe second embodiment. FIG. 6 is a sectional view showing the layerstructure of one pixel of the radiation image sensing apparatusaccording to the second embodiment. FIGS. 4 and 5 show an example inwhich 4 (rows)×4 (columns) (=a total of 16) pixels are arranged in apixel area, as in the first embodiment. However, the number of pixels isnot limited to this. For example, 2,000×2,000 pixels may be arranged.

In this embodiment, a combination of a PIN photoelectric conversionelement (first semiconductor conversion element) and a read TFT (switchelement) or a combination of a PIN photoelectric conversion element(first semiconductor conversion element), read TFT (switch element), andPIN sensor (second semiconductor conversion element) for AEC is arrangedfor each pixel. More specifically, a pixel on the ath row and the bthcolumn from the upper side in FIGS. 4 and 5 has one photoelectricconversion element Pba and one thin film transistor Tba (a, b=1, 2, 3,4). A pixel on the ath row and the third column also has one PIN sensorPA3 a.

Four PIN photoelectric conversion elements arranged on the bth columnare connected to a common bias line Vsb so that a predetermined bias isapplied from a reading unit. The gate electrodes of four read TFTsarranged on the ath row are connected to a common gate line Vga so thatthe gates are ON/OFF-controlled by a gate driving unit. The sourceelectrodes or drain electrodes of the four read TFTs arranged on the bthcolumn are connected to a common signal line Sigb. Signal lines Sig1 toSig4 are connected to the reading unit.

The layer structure of the pixel having the PIN sensor will be describedhere with reference to FIG. 6. This pixel has an etching-stopper-typeread TFT 4, PIN photoelectric conversion element 5, and PIN sensor 6.

As the layer structure of this pixel, a gate electrode 12 for the readTFT 4 and a first insulating layer 13 which covers the gate electrode 12are formed on an insulating substrate 11. The first insulating layer 13functions as the gate insulating film of the read TFT 4.

A semiconductor layer (channel layer) 14 of the read TFT 4 is formed onthe first insulating layer 13. A fourth insulating layer 31 is formed onthe semiconductor layer 14. Ohmic contact layers 15 that sandwich thefourth insulating layer 31 are formed. One of the ohmic contact layers15 is formed to extend from the fourth insulating layer 31 andsemiconductor layer 14 to the first insulating layer 13. Source anddrain electrodes 16 are formed on the ohmic contact layers 15,respectively. A second insulating layer 18 that covers the source anddrain electrodes 16 is formed.

A contact hole is formed in the second insulating layer 18 and reachesone of the source and drain electrodes 16, which extends on the firstinsulating layer 13. A lower electrode 32 of the PIN photoelectricconversion element 5 is formed on the second insulating layer 18 andconnected to one of the source and drain electrodes 16 through thecontact hole. An n-semiconductor layer 33, intrinsic semiconductor layer34, and p-semiconductor layer 35 are sequentially formed on the lowerelectrode 32. An upper electrode 36 of the PIN photoelectric conversionelement 5 is formed on the p-semiconductor layer 35.

A lower electrode 37 of the PIN sensor 6 is also formed on the secondinsulating layer 18. An n-semiconductor layer 38, intrinsicsemiconductor layer 39, and p-semiconductor layer 40 are sequentiallyformed on the lower electrode 37. As will be described later, then-semiconductor layers 33 and 38 are formed from the same layer. Theintrinsic semiconductor layers 34 and 39 are formed from the same layer.The p-semiconductor layers 35 and 40 are formed from the same layer. Anupper electrode 41 of the PIN sensor 6 is formed on the p-semiconductorlayer 40. A third insulating layer 25 that covers the upper electrodes36 and 41 is formed.

An organic protective layer 26, adhesive layer 27, and phosphor layer 28are sequentially formed on the third insulating layer 25, as in thefirst embodiment.

As the read TFT 4, a TFT with a high transfer speed is preferably used.Hence, the semiconductor layer 14 is a thin film. On the other hand, thePIN photoelectric conversion element 5 and PIN sensor 6 can preferablyabsorb incident light sufficiently. Hence, the intrinsic semiconductorlayers 34 and 39 are preferably thicker than the semiconductor layer 14.A TFT made of polysilicon may be used.

In the layer structure of a pixel that has no PIN sensor 6, the lowerelectrode 37, n-semiconductor layer 38, intrinsic semiconductor layer39, p-semiconductor layer 40, and upper electrode 41 are omitted fromthe structure shown in FIG. 6.

The upper electrode 36 of the PIN photoelectric conversion element 5 isconnected to a bias line. One of the source and drain electrodes 16,which is not connected to the lower electrode 32, is connected to asignal line. The gate electrode 12 is connected to a gate line. In thePIN sensor 6, the lower electrode 37 and upper electrode 41 areconnected to a reading unit.

The operation of the radiation image sensing apparatus according to thesecond embodiment having the above arrangement will be described next.

When an object such as a human body to be inspected is exposed to X-rayson this radiation image sensing apparatus, the X-rays pass through theobject to be inspected while being attenuated by it. The X-rays areconverted into visible light by the phosphor layer 28. The visible lightstrikes the PIN photoelectric conversion element 5 and is converted intocharges. The charges are transferred to the signal line through the readTFT 4 in accordance with a gate driving pulse applied from a gatedriving unit and output to the outside through the reading unit.

For the PIN sensor 6, for example, a predetermined bias is appliedbetween the lower electrode 37 and the upper electrode 41 in advance.When a predetermined bias is applied in advance, charges correspondingto incident light are always output. When the output value is amplifiedby an amplifier (AMP) and added, the total X-ray dose can be detected bythe reading unit. X-ray exposure is controlled on the basis of the totalX-ray dose.

Even in the second embodiment, the same effect as in the firstembodiment can be obtained. In the second embodiment, since the lowerelectrode 32 of the PIN photoelectric conversion element 5 is largerthan the lower electrode (one of the source and drain electrodes 16) ofthe MIS photoelectric conversion element 2 in the first embodiment,radiation can be detected at a higher efficiency.

The PIN sensor 6 can be selectively laid out at a necessary position.That is, not all the PIN sensor 6 need be laid out on one column ofpixels, unlike FIG. 4. In a pixel having the PIN sensor 6, the openingratio of the PIN photoelectric conversion element 5 decreases. However,the decrease in area can easily be compensated by image correction afterthe read.

A method of manufacturing the radiation image sensing apparatusaccording to the second embodiment will be described next.

First, a first electrode layer is formed on the insulating substrate 11and patterned to form the gate electrode 12. Next, the first insulatinglayer 13 is formed on the entire surface.

A first semiconductor layer is formed on the first insulating layer 13and patterned to form the semiconductor layer 14. The fourth insulatinglayer 31 is formed at the center of the semiconductor layer 14. Then,the ohmic contact layers 15 are formed on the semiconductor layer 14.Subsequently, a second electrode layer is formed on the entire surfaceand patterned to form the source and drain electrodes 16. The secondinsulating layer 18 is formed on the entire surface. The contact holethat reaches one of the source and drain electrodes 16 is formed in thesecond insulating layer 18.

A fourth electrode layer that fills the contact hole is formed andpatterned to form the lower electrodes 32 and 37 simultaneously. Thirdto fifth semiconductor layers are formed on the entire surface andpatterned to form the n-semiconductor layers 33 and 38 simultaneously,the intrinsic semiconductor layers 34 and 39 simultaneously, and thep-semiconductor layers 35 and 40 simultaneously. Subsequently, a fifthelectrode layer is formed on the entire surface and patterned to formthe upper electrodes 36 and 41. The third insulating layer 25 is formedon the entire surface.

After that, the organic protective layer 26, adhesive layer 27, andphosphor layer 28 are sequentially formed on the entire surface.

In this way, the radiation image sensing apparatus according to thesecond embodiment can be manufactured.

Instead of forming the PIN photoelectric conversion element 5 and PINsensor 6, an insulating film may be formed on the lower electrode 33,and a MIS photoelectric conversion element and TFT sensor may be formedon the insulating film.

Third Embodiment

The third embodiment of the present invention will be described next. Inthis embodiment, a combination of a photoconductive element (firstphotoconductive element), read TFT (switch element), and image sensingcapacitor (capacitive element) or a combination of a photoconductiveelement (first photoconductive element), read TFT (switch element),image sensing capacitor (capacitive element), and photoconductive sensor(second photoconductive element) for AEC is arranged for each pixel.

The layer structure of a pixel having a photoconductive sensor will bedescribed here with reference to FIG. 7. FIG. 7 is a sectional viewshowing the layer structure of one pixel of a radiation image sensingapparatus according to the third embodiment of the present invention.This pixel has an etching-stopper-type read TFT 4, photoconductiveelement 7, photoconductive sensor 8, and image sensing capacitor 9. Thestructure of the read TFT 4 is the same as in the second embodiment.

As the layer structure of this pixel, a gate electrode 12 for the readTFT 4, a lower electrode 42 of the image sensing capacitor 9, and afirst insulating layer 13 which covers the electrodes 12 and 42 areformed on an insulating substrate 11. The first insulating layer 13functions as the gate insulating film of the read TFT 4.

A semiconductor layer (channel layer) 14 of the read TFT 4 is formed onthe first insulating layer 13 to be aligned with the gate electrode 12when viewed from the upper side. A fourth insulating layer 31 is formedon the semiconductor layer 14. Ohmic contact layers 15 that sandwich thefourth insulating layer 31 are formed. One of the ohmic contact layers15 is formed to extend from the fourth insulating layer 31 andsemiconductor layer 14 to the first insulating layer 13 and be alignedwith the lower electrode 42 when viewed from the upper side. Source anddrain electrodes 16 are formed on the ohmic contact layers 15,respectively. A second insulating layer 18 that covers the source anddrain electrodes 16 is formed. The second insulating layer 18 is madeof, e.g., BCB (benzocyclobutene).

A contact hole is formed in the second insulating layer 18 and reachesone of the source and drain electrodes 16, which extends on the firstinsulating layer 13. A lower electrode (charge collection electrode) 43of the photoconductive element 7 is formed on the second insulatinglayer 18 and connected to one of the source and drain electrodes 16through the contact hole. A lower electrode (charge collectionelectrode) 44 of the photoconductive sensor 8 is also formed on thesecond insulating layer 18. An amorphous selenium layer 45 that coversthe lower electrodes 43 and 44 is formed. The amorphous selenium layer45 is shared by the photoconductive element 7 and photoconductive sensor8.

An upper electrode (common electrode) 46, fifth insulating layer 47, andorganic protective layer 48, which are shared by the photoconductiveelement 7 and photoconductive sensor 8, are formed on the amorphousselenium layer 45. The lower electrode 44 and upper electrode 46 may bemade of, e.g., a p- or n-semiconductor.

In the layer structure of a pixel that has no photoconductive sensor 8,the lower electrode 44 is omitted from the structure shown in FIG. 7.

The upper electrode 46 is shared by pixels and connected to a bias line.One of the source and drain electrodes 16, which is not connected to thelower electrode 43, is connected to a signal line. The gate electrode 12is connected to a gate line. In the photoconductive sensor 8, the lowerelectrode 44 is connected to a reading unit.

The operation of the radiation image sensing apparatus according to thethird embodiment having the above arrangement will be described next.

When an object such as a human body to be inspected is exposed to X-rayson this radiation image sensing apparatus, the X-rays pass through theobject to be inspected while being attenuated by it. The X-rays becomeincident on the amorphous selenium layer 45. In the amorphous seleniumlayer 45, positive charges and negative charges in an amountcorresponding to the energy of the incident X-rays are generated by aninternal photoelectric effect (photoconductive effect). In thisembodiment, a voltage of several kV is applied between the upperelectrode 46 and the lower electrode 43 in advance. In such a voltageapplied state, charges are generated in the amorphous selenium layer 45by the photoconductive effect, as described above. Since the chargesmove along the electric field, a photocurrent is generated. When thephotocurrent is generated, charges are stored in the image sensingcapacitor 9. The charges are transferred to the signal line through theread TFT 4 in accordance with a gate driving pulse applied from a gatedriving unit and output to the outside through the reading unit.

For the photoconductive sensor 8, for example, a predetermined bias isapplied between the upper electrode 46 and the lower electrode 44 inadvance. When a predetermined bias is applied in advance, chargescorresponding to the energy of incident X-rays are always output. Whenthe output value is amplified by an amplifier (AMP) and added, the totalX-ray dose can be detected by the reading unit. X-ray exposure iscontrolled on the basis of the total X-ray dose.

Even in the third embodiment, the same effect as in the first and secondembodiments can be obtained.

The photoconductive sensor 8 can be selectively laid out at a necessaryposition. In a pixel having the photoconductive sensor 8, the openingratio of the photoconductive element 7 decreases. However, the decreasein area can easily be compensated by image correction after the read.

In this embodiment, the ohmic contact layers 15 or organic protectivelayer 48 may be omitted.

A method of manufacturing the radiation image sensing apparatusaccording to the third embodiment will be described next.

First, a first electrode layer is formed on the insulating substrate 11and patterned to form the gate electrode 12 and lower electrode 42.Next, the first insulating layer 13 is formed on the entire surface.

A first semiconductor layer is formed on the first insulating layer 13and patterned to form the semiconductor layer 14. The fourth insulatinglayer 31 is formed at the center of the semiconductor layer 14. Then,the ohmic contact layers 15 are formed on the semiconductor layer 14.Subsequently, a second electrode layer is formed on the entire surfaceand patterned to form the source and drain electrodes 16. The secondinsulating layer 18 made of, e.g., BCB is formed on the entire surface.The contact hole that reaches one of the source and drain electrodes 16is formed in the second insulating layer 18. The second insulating layer18 is planarized.

A sixth electrode layer that fills the contact hole is formed andpatterned to form the lower electrodes 43 and 44. The amorphous seleniumlayer 45 is formed on the entire surface. The upper electrode 46 servingas a seventh electrode layer is formed on the entire surface.

The fifth insulating layer 47 and organic protective layer 48 aresequentially formed on the entire surface.

In this way, the radiation image sensing apparatus according to thethird embodiment can be manufactured.

Fourth Embodiment

The fourth embodiment of the present invention will be described next.In this embodiment, a combination of a photoconductive element (firstphotoconductive element), read TFT (switch element), and image sensingcapacitor (capacitive element) or a combination of a photoconductiveelement (first photoconductive element), read TFT (switch element),image sensing capacitor (capacitive element), photoconductive sensor(second photoconductive element), and AEC capacitor is arranged for eachpixel.

The layer structure of a pixel having a photoconductive sensor will bedescribed here with reference to FIG. 8. FIG. 8 is a sectional viewshowing the layer structure of one pixel of a radiation image sensingapparatus according to the fourth embodiment of the present invention.This pixel has an etching-stopper-type read TFT 4, photoconductiveelement 7, photoconductive sensor 8, image sensing capacitor 9, and AECcapacitor 10. The structures of the read TFT 4, photoconductive element7, photoconductive sensor 8, and image sensing capacitor 9 are the sameas in the third embodiment, and a description thereof will be omitted.

The AEC capacitor 10 has a lower electrode 49 formed on an insulatingsubstrate 11, and a conductive layer 50 and upper electrode 51, whichare sequentially formed on a first insulating layer 13. A contact holethat reaches the upper electrode 51 is formed in the second insulatinglayer 18. A lower electrode 44 is connected to the upper electrode 51through the contact hole.

In this embodiment, for the photoconductive sensor 8 and AEC capacitor10, not the lower electrode 44 but the upper electrode 51 or conductivelayer 50 is connected to a reading unit, unlike the third embodiment.

The operation of the radiation image sensing apparatus according to thefourth embodiment having the above arrangement will be described next.

When an object such as a human body to be inspected is exposed to X-rayson this radiation image sensing apparatus, the X-rays pass through theobject to be inspected while being attenuated by it. The X-rays becomeincident on an amorphous selenium layer 45. In the amorphous seleniumlayer 45, positive charges and negative charges in an amountcorresponding to the energy of the incident X-rays are generated by aninternal photoelectric effect (photoconductive effect). Even in thisembodiment, a voltage of several kV is applied between an upperelectrode 46 and a lower electrode 43 in advance. In such a voltageapplied state, charges are generated in the amorphous selenium layer 45by the photoconductive effect, as described above. Since the chargesmove along the electric field, a photocurrent is generated. When thephotocurrent is generated, charges are stored in the image sensingcapacitor 9. The charges are transferred to the signal line through theread TFT 4 in accordance with a gate driving pulse applied from a gatedriving unit and output to the outside through the reading unit.

For the photoconductive sensor 8, for example, a predetermined bias isapplied between the upper electrode 46 and the lower electrode 44 inadvance. When a predetermined bias is applied in advance, chargescorresponding to the energy of incident X-rays are always output throughthe AEC capacitor 10. When the output value is amplified by an amplifier(AMP) and added, the total X-ray dose can be detected by the readingunit. X-ray exposure is controlled on the basis of the total X-ray dose.

Even in the fourth embodiment, the same effect as in the first to thirdembodiments can be obtained.

The photoconductive sensor 8 and AEC capacitor 10 can be selectivelylaid out at necessary positions. In a pixel having the photoconductivesensor 8 and AEC capacitor 10, the opening ratio of the photoconductiveelement 7 decreases. However, the decrease in area can easily becompensated by image correction after the read.

In this embodiment, ohmic contact layers 15, the conductive layer 50, oran organic protective layer 48 may be omitted.

A method of manufacturing the radiation image sensing apparatusaccording to the fourth embodiment will be described next. The lowerelectrode 49 can be formed simultaneously with a gate electrode 12 andlower electrode 42 by patterning a first electrode layer. The conductivelayer 50 can be formed simultaneously with the ohmic contact layers 15.The upper electrode 51 can be formed simultaneously with source anddrain electrodes 16 by patterning a second electrode layer. The contacthole that reaches the upper electrode 51 can be formed simultaneouslywith a contact hole that reaches one of the source and drain electrodes16. The remaining constituent elements are formed in accordance with thesame procedures as in the third embodiment.

In this way, the radiation image sensing apparatus according to thefourth embodiment can be manufactured.

In the third and fourth embodiments, another layer such as a galliumarsenide layer having a photoconductive effect may be formed in place ofthe amorphous selenium layer 45.

According to the above-described first to fourth embodiments, AEC can beexecuted on the basis of a radiation dose detected through a secondsemiconductor conversion element or second photoconductive element. Thesecond semiconductor conversion element or second photoconductiveelement is formed on the same substrate as the first semiconductorconversion element or first photoconductive element. Hence, anyradiation attenuation by the second semiconductor conversion element orsecond photoconductive element can be prevented. The first semiconductorconversion element or first photoconductive element need not be used forAEC and therefore need not be driven at a high speed. Hence, the chargestorage time, charge transfer time, and capacitor reset time can besufficiently ensured. For this reason, according to the presentinvention, an image with a high image quality can be sensed.

Fifth Embodiment

The fifth embodiment of the present invention will be described next. Inthis embodiment, a drain electrode 222 d is connected to a commonelectrode bias line 216 to omit a lead interconnection 224 of the drainelectrode 222 d. With this structure, the light-receiving area (openingratio) of an image sensing photoelectric conversion element 1 in a pixelhaving a lead interconnection is increased to improve thecharacteristics. FIG. 18 is a layout diagram showing the planarstructure of a pixel of a radiation image sensing apparatus according tothis embodiment, which has a monitor photoelectric conversion element.FIG. 19 is a layout diagram showing the planar structure of a pixel ofthe radiation image sensing apparatus according to this embodiment,which has lead interconnections for a monitor photoelectric conversionelement. FIG. 20 is a sectional view taken along a line II-II in FIG.18. FIG. 21 is a schematic view showing the layout of a conversionsection T and circuit sections around it.

In this embodiment, in a pixel having a TFT monitor photoelectricconversion element, a drain electrode 122 d is connected to a commonelectrode bias line 116, as shown in FIG. 18.

Pixels each having the above structure are collectively laid out, as inthe area R2 of the reference example. For example, the drain electrode122 d, a source electrode 122 s, the common electrode bias line 116, anda signal line 119 are shared by these pixels.

In a pixel having lead interconnections for a monitor photoelectricconversion element, an interconnection 125 for a control electrode 121and an interconnection 126 for the source electrode 122 s are formed, asshown in FIG. 19. Unlike the reference example, no interconnection forthe drain electrode 122 d is formed. This is because the drain electrode122 d is connected to the common electrode bias line 116. Theinterconnections 125 and 126 are connected between pixels that areadjacent and are located at the outermost portion of the conversionsection T. The source electrode 122 s and control electrode 121 are ledto the outside of the panel by the interconnections 125 and 126.

A pixel which has neither a monitor photoelectric conversion element norlead interconnections therefor has the same structure as that of thepixel shown in FIGS. 14 and 17 (the pixel of the reference example).

The pixel shown in FIGS. 18 and 20 will be compared with that shown inFIGS. 14 and 17. The shapes and areas of the pixels are the same. In thepixel shown in FIGS. 18 and 20, since a monitor photoelectric conversionelement 102 is formed, the light-receiving area (opening ratio) of animage sensing photoelectric conversion element 101 decreases. The pixelshown in FIG. 19 will be compared with that shown in FIGS. 14 and 17.The shapes and areas of the pixels are the same. Since theinterconnections 125 and 126 are formed, the light-receiving area(opening ratio) of the image sensing photoelectric conversion element101 decreases.

These pixels are laid out as shown in FIG. 13, as in the referenceexample. That is, areas R2 where a plurality of pixels each made of apair of monitor photoelectric conversion element and image sensingphotoelectric conversion element are formed are laid out at the fourcorners and near the center of the conversion section T having atwo-dimensional rectangular shape. In this embodiment, monitorphotoelectric conversion elements are formed in 20 (rows)×3 (columns)pixels in each area R2.

A method of driving the radiation image sensing apparatus according tothis embodiment, which has the above-described arrangement, will bedescribed next.

First, as described above, a voltage is applied from a common electrodedriver circuit 156 to the common electrode bias line 116 to apply apotential between the source and the drain of the monitor photoelectricconversion element 102. In addition, the depletion voltage of asemiconductor layer 114 c is applied to the control electrode 121 toprevent a dark current and increase the electron/hole collectionefficiency.

In this state, the phosphor layer (not shown) is irradiated with X-rays.The photoelectric conversion section is irradiated with visible lightfrom the phosphor layer. The visible light absorbed by the monitorphotoelectric conversion element 102 is converted into charges andtransported to a monitor signal processing circuit 154 through thesource electrode 122 s. For this reason, the charge amount can bemeasured in real time as an X-ray dose.

When the X-ray dose measured by the monitor signal processing circuit154 reaches a set value, a signal is sent to the X-ray generator(radiation source) to stop X-ray irradiation. Immediately after that,the operating voltage of a TFT 103 is sequentially applied to gate lines120 of the TFTs 103, thereby reading charges stored in the capacitors ofthe image sensing photoelectric conversion elements 101 from signallines 119.

After that, a forward voltage is applied to a semiconductor layer 114 aof the image sensing photoelectric conversion element 101 through thecommon electrode bias line 116. Accordingly, a refresh operation isperformed. That is, all charges stored in the interface between aninsulating film 113 and the semiconductor layer 114 a in the imagesensing photoelectric conversion element 101 in correspondence with theX-ray dose are removed.

A voltage with which a forward voltage is applied to the semiconductorlayer 114 c in accordance with the voltage applied to the commonelectrode bias line 116 is applied to the control electrode 121 of themonitor photoelectric conversion element 102 in advance. When thisvoltage is applied to the control electrode 121 in advance, a voltagefor the refresh operation of the image sensing photoelectric conversionelement 101 is applied to the drain electrode 122 d of the monitorphotoelectric conversion element 102 connected to the common electrodebias line 116. Simultaneously, the forward voltage is also applied tothe semiconductor layer 114 c in the monitor photoelectric conversionelement 102. Hence, the refresh operation for the monitor photoelectricconversion element 102 is also executed.

In the refresh operation, not all the stored charges but some of themmay be removed. A voltage that decreases a depletion bias may be appliedto the common electrode bias line 116. In the refresh operation, thevoltage of the source electrode 122 s may be controlled to set a stateto easily remove the charges.

In the reference example, three lead interconnections 124 to 126 areformed. In this embodiment, however, the lead interconnection 124 forthe drain electrode is not formed. Instead, only the two leadinterconnections 125 and 126 are formed. Hence, according to thisembodiment, the light-receiving area (opening ratio) of the imagesensing photoelectric conversion element 101 in this pixel is large.Furthermore, in the reference example, the power supply 153 to supply avoltage to the drain electrode 122 d is necessary. In this embodiment,however, since the voltage is supplied from the common electrode drivercircuit 156 through the common electrode bias line 116, no power supplyis necessary. Hence, the circuit can be simplified.

Some pixels may have no image sensing photoelectric conversion elements101 and only the monitor photoelectric conversion elements 102 and leadinterconnections for the monitor photoelectric conversion elements 102in adjacent pixels. In this case, data from the image sensingphotoelectric conversion elements 101 decreases. The decrease must becompensated by image processing. This compensation can be done by aconventional image processing technique.

Alternatively, only the pixels of one line in each area R2, and forexample, only 20 (rows)×1 (column) pixels or 1 (row)×3 (columns) pixelsin the area R2 may have the monitor photoelectric conversion elements.

A method of manufacturing the radiation image sensing apparatusaccording to this embodiment will be described next. FIGS. 22A to 22Dand 23A to 23C are sectional views showing steps in manufacturing theradiation image sensing apparatus according to this embodiment.

First, as shown in FIG. 22A, an AlNd film 131 serving as a first metallayer and having a thickness of 500 to 4,000 Å is formed on aninsulating substrate 110 by, e.g., sputtering. An Mo film or Ta film maybe formed as the first metal layer. Alternatively, a multilayered filmmay be formed by sequentially forming a plurality of films. Next, theAlNd film 131 is patterned by photolithography using a resist film 132as a mask to form a sensor electrode 111, the control electrodes 112 and121, and gate line 120. Etching of the AlNd film 131 is done by a wetprocess using an etchant containing, e.g., nitric acid, phosphoric acid,and acetic acid. After patterning, the resist film 132 is removed.

As shown in FIG. 22B, the first insulating film 113 having a thicknessof 1,500 to 4,000 Å and a semiconductor layer 133 having a thickness of2,000 to 15,000 Å are continuously formed by CVD. The semiconductorlayer 133 becomes the semiconductor layer (photoelectric conversionlayer) 114 a of the image sensing photoelectric conversion element 101,a semiconductor layer 114 b of a TFT 103, and the semiconductor layer(photoelectric conversion layer) 114 c of the monitor photoelectricconversion element 102. As the first insulating film 113, for example,an SiN film is used.

Then, the semiconductor layer 133 is etched not entirely but partiallyby only 500 to 5,000 Å by photolithography using a resist film 134having an opening on the control electrode 112 of the TFT 103 as a mask.The semiconductor layer 133 is formed as thick as 2,000 to 15,000 Å toincrease the optical absorption efficiency in the image sensingphotoelectric conversion element 101 and monitor photoelectricconversion element 102. In this state, the series resistance between thesource and the drain of the TFT 103 is high. Hence, the process forthinning the semiconductor layer 133 is executed to reduce the ONresistance of the TFT 103. At this time, the semiconductor layer 133 isetched by, e.g., dry etching. As dry etching, plasma etching ispreferably used because a high process accuracy can be obtained whileminimizing damage to the semiconductor layer 133. Chemical dry etchingwhich can also minimize damage to the semiconductor layer 133 may beused. Alternatively, reactive ion etching at a low power (e.g., about0.1 to 0.2 W/cm²) and high pressure (e.g., about 10 to 30 Pa) may beperformed. After patterning, the resist film 134 is removed.

As shown in FIG. 22C, an ohmic contact layer 135 having a thickness of100 to 1,000 Å is formed by CVD. If silicon oxide is present in theinterface between the semiconductor layer 133 and the ohmic contactlayer 135, a preprocess using hydrofluoric acid (e.g., about 0.1 to 10wt %) may be executed. If an organic film is inserted, it may be removedby irradiating it with oxygen plasma. In addition, a final process usinghydrogen plasma may be executed in the CVD apparatus immediately beforeformation of the ohmic contact layer 135.

Next, a through hole 127 is formed by photolithography using a resistfilm 136 as a mask. The through hole 127 electrically connects a drainelectrode 117 d of the TFT 103 to the sensor electrode 111 of the imagesensing photoelectric conversion element 101. Charges generated when thelight-receiving portion absorbs visible light are read, through thedrain electrode 117 d, from the sensor electrode 111 capacitivelycoupled to the light-receiving portion.

To improve the coverage of a metal film to be formed later, chemical dryetching is preferably performed to form a hole having a tapered section.If the coverage of the metal film need not be taken into consideration,the process accuracy may be increased by reactive ion etching.Alternatively, the hole may be formed by plasma etching. Afterpatterning, the resist film 136 is removed.

As shown in FIG. 22D, an Al film 137 serving as a second metal layer andhaving a thickness of 1,000 to 10,000 Å is formed by, e.g., sputtering.An Mo film or Ta film may be formed as the second metal layer.Alternatively, a multilayered film may be formed by sequentially forminga plurality of films. If an oxide film is formed on the surface of thethrough hole 127, and satisfactory connection to the through hole 127cannot be ensured, a process for removing the oxide film by reversesputtering is inserted before formation of the Al film 137.

The Al film 137 is patterned by photolithography using a resist film 138as a mask to form the common electrode bias line 116. Etching of the Alfilm 137 is done by a wet process using an etchant containing, e.g.,nitric acid, phosphoric acid, and acetic acid. Hence, the Al film 137 isetched slightly inward under the resist film 138. In this patterning,the Al film 137 in regions where the source electrodes 117 s and 122 s,drain electrodes 117 d and 122 d, and signal line 119 are to be formedis masked by the resist film 138 to prevent etching in this process.After patterning, the resist film 138 is removed.

After that, as shown in FIG. 23A, the Al film 137 is patterned byphotolithography using a new resist film 139 as a mask to form thesource electrodes 117 s and 122 s, drain electrodes 117 d and 122 d, andsignal line 119. Etching of the Al film 137 is done by a wet processusing an etchant containing, e.g., nitric acid, phosphoric acid, andacetic acid. Hence, the Al film 137 is etched slightly inward under theresist film 139.

At this time, the common electrode bias line 116 that has already beenformed is masked by the resist film 139 to prevent etching in thisprocess. In addition, to prevent the ohmic contact layer 135 in theopening region of the image sensing photoelectric conversion element 101from being removed by dry etching of the next process, not only thecommon electrode bias line 116 but also the entire opening region of theimage sensing photoelectric conversion element 101 is masked by theresist film 139.

As shown in FIG. 23A, dry etching is performed using the resist film 139as a mask to remove the gap portions of the TFT 103, i.e., the ohmiccontact layer 135 between the sources and the drains, thereby formingohmic contact layers 115 a to 115 c.

As shown in FIG. 23B, unnecessary portions of the semiconductor layer133 and ohmic contact layer 135 are removed by photolithography using aresist film 140 as a mask to define the opening region of the imagesensing photoelectric conversion element 101 and form the semiconductorlayers 114 a to 114 c. After patterning, the resist film 140 is removed.

The unnecessary portions of the first insulating film 113 are notremoved in this embodiment. However, they may be removed. When the firstinsulating film 113 is left without being removed, the etching processfor removing the unnecessary portions of the semiconductor layer 133 andohmic contact layer 135 is preferably executed by using plasma etchingin order to ensure the process accuracy because the selectivity ratiobetween the semiconductor layer 133 and the SiN film that constitutesthe first insulating film 113 can readily be ensured in plasma etching.

As shown in FIG. 23C, a second insulating film 118 serving as aprotective film and having a thickness of 2,000 to 10,000 Å is formed byCVD. As the second insulating film 118, for example, an SiN film can beformed. In this way, the image sensing photoelectric conversion element101, monitor photoelectric conversion element 102, and TFT 103 can beformed.

A phosphor layer (not shown) is formed. To ensure electrical connection,the protective film at the periphery is removed by patterning and dryetching using photolithography. Thus, a radiation image sensingapparatus can be completed.

In the above description of the method of manufacturing the radiationimage sensing apparatus according to this embodiment, to make the ohmiccontact layer function as an upper electrode (first electrode), thesecond metal film is formed after formation of the ohmic contact layer.When the resistivity of the ohmic contact layer is high, a transparentelectrode film made of, e.g., ITO (Indium Tin Oxide) may be formed onthe ohmic contact layer before formation of the second metal film. Inthis case, both the first and second electrodes have a multilayeredstructure of the ohmic contact layer and transparent electrode film.When such a transparent electrode film is formed, no problem is formedeven when the ohmic contact layer is thin. Since the ohmic contact layercan be thin, the incident light amount itself can be increased. Even inthe monitor photoelectric conversion element 102, when a transparentelectrode film is used for the source electrode 122 s and drainelectrode 122 d, the incident light amount can be increased. Hence, thesensitivity of the monitor photoelectric conversion element 102increases.

Sixth Embodiment

The sixth embodiment of the present invention will be described next. Inthe fifth embodiment, the monitor photoelectric conversion element 102is a TFT sensor. In this embodiment, a monitor photoelectric conversionelement 102 is a MIS sensor. In a MIS sensor, the voltage between twoelectrodes varies due to the influence of electrons and holes generatedin a semiconductor layer when visible light is incident. The variationin voltage is read, or a variation in current based on the variation involtage is read. FIG. 24 is a layout diagram showing the overallarrangement of a radiation image sensing apparatus according to thisembodiment. FIG. 25 is a layout diagram showing the planar structure ofa pixel of the radiation image sensing apparatus according to thisembodiment, which has a monitor photoelectric conversion element. FIG.26 is a layout diagram showing the planar structure of a pixel of theradiation image sensing apparatus according to this embodiment, whichhas lead interconnections for a monitor photoelectric conversionelement. FIG. 27 is a sectional view taken along a line III-III in FIG.25.

In this embodiment, areas R1, R2, and R3 are arranged in a conversionsection (pixel area) T, as in the fifth embodiment. However, the layoutis different from the fifth embodiment, as shown in FIG. 24. In thisembodiment, the area R3 is laid out in a direction in which a gate line120 runs with respect to the area R2. In addition, neither a powersupply 153 nor a gate driver circuit 155 is arranged. This is becausethe monitor photoelectric conversion element 102 is a MIS sensor. Inthis embodiment, monitor photoelectric conversion elements are formed in3 (rows)×20 (columns) pixels in each area R2.

In this embodiment, the sectional structures of an image sensingphotoelectric conversion element 101 and switching TFT 103 are the sameas in the fifth embodiment except that a transparent electrode 162 a isformed between an ohmic contact layer 115 a and a common electrode biasline 116 in the image sensing photoelectric conversion element 101, asshown in FIG. 27. That is, in this embodiment, the upper electrode(first electrode) has a multilayered structure of an ohmic contact layerand transparent electrode. The structure of a pixel which has neither amonitor photoelectric conversion element nor lead interconnectionstherefor is the same as in the fifth embodiment.

On the other hand, in a pixel having a monitor photoelectric conversionelement, as shown in FIG. 25, in addition to a sensor electrode 111 ofthe image sensing photoelectric conversion element 101 and a controlelectrode (gate electrode) 112 of the switching TFT 103, a lowerelectrode 161 of the monitor photoelectric conversion element 102 isformed on an insulating substrate 110. These electrodes are covered witha first insulating film 113. In this embodiment, the monitorphotoelectric conversion element 102 is laid out to be adjacent to theimage sensing photoelectric conversion element 101 in the pixel alongthe direction in which the common electrode bias line 116 runs. Thispixel will be compared with the pixel which has neither a monitorphotoelectric conversion element nor lead interconnections therefor (thepixel shown in FIGS. 14 and 17). The shapes and areas of the pixels arethe same. In the pixel shown in FIG. 25, since the lower electrode 161is formed, the sensor electrode 111 and the like are smaller.

In the monitor photoelectric conversion element 102, as shown in FIG.27, a semiconductor layer (photoelectric conversion layer) 114 c isformed on the insulating film 113 to be aligned with the lower electrode161. An ohmic contact layer 115 c and transparent electrode 162 c areformed on the semiconductor layer 114 c. An upper electrode (secondelectrode) is formed from the ohmic contact layer 115 c and transparentelectrode 162 c. The common electrode bias line 116 is formed on thetransparent electrode 162 c. The common electrode bias line 116 iscovered with a second insulating film 118.

A pixel having the above structure is present in the area R2 shown inFIG. 24.

A pixel having lead interconnections for a monitor photoelectricconversion element has an interconnection 163 for the lower electrode161, as shown in FIG. 26. The interconnection 163 runs in parallel tothe gate line 120. The interconnection 163 is laid out to be adjacent tothe image sensing photoelectric conversion element 101 in the pixelalong the direction in which the common electrode bias line 116 runs.This pixel will be compared with the pixel which has neither a monitorphotoelectric conversion element nor lead interconnections therefor (thepixel shown in FIGS. 14 and 17). The shapes and areas of the pixels arethe same. In the pixel shown in FIG. 26, since the interconnection 163is formed, the sensor electrode 111 and the like are smaller. Theinterconnection 163 is connected between pixels that are adjacent andare located at the outermost portion of the conversion section T. Thatis, when an array of pixels that share the gate line 120 is defined as a“row”, all or some of the lower electrodes 161 of the monitorphotoelectric conversion elements 102 arranged on the same row areconnected to each other through the interconnection 163. The lowerelectrodes 161 are led to the outside of the panel by theinterconnection 163.

A pixel having the above structure is present in the area R3 shown inFIG. 24.

A method of driving the radiation image sensing apparatus according tothis embodiment, which has the above-described arrangement, will bedescribed next.

First, the depletion voltage of the semiconductor layers 114 a and 114 cis applied from a common electrode driver circuit 156 to the commonelectrode bias line 116 to increase the electron/hole collectionefficiency.

In this state, the phosphor layer (not shown) is irradiated with X-rays.The photoelectric conversion section is irradiated with visible lightfrom the phosphor layer. The visible light absorbed by the monitorphotoelectric conversion element 102 is converted into charges. Apotential variation of the monitor photoelectric conversion element 102based on the charges or a current value based on the potential variationis transported to a monitor signal processing circuit 154. For thisreason, the potential variation or current value can be measured in realtime as an X-ray dose.

When the X-ray dose measured by the monitor signal processing circuit154 reaches a set value, a signal is sent to the X-ray generator(radiation source) to stop X-ray irradiation. Immediately after that,the operating voltage of the TFT 103 is sequentially applied to the gatelines 120 of the TFTs 103, thereby reading charges stored in thecapacitors of the image sensing photoelectric conversion elements 101from signal lines 119.

After that, a forward voltage is applied to the semiconductor layer 114a of the image sensing photoelectric conversion element 101 through thecommon electrode bias line 116. Accordingly, a refresh operation isperformed. That is, all charges stored in the interface between theinsulating film 113 and the semiconductor layer 114 a in the imagesensing photoelectric conversion element 101 in correspondence with theX-ray dose are removed.

A voltage with which a forward voltage is applied to the semiconductorlayer 114 c in accordance with the voltage applied to the commonelectrode bias line 116 is applied to the lower electrode 161 of themonitor photoelectric conversion element 102 in advance. When thisvoltage is applied to the lower electrode 161 in advance, a voltage forthe refresh operation of the image sensing photoelectric conversionelement 101 is applied to the transparent electrode 162 c of the monitorphotoelectric conversion element 102 connected to the common electrodebias line 116. Simultaneously, the forward voltage is also applied tothe semiconductor layer 114 c in the monitor photoelectric conversionelement 102. Hence, the refresh operation for the monitor photoelectricconversion element 102 is also executed.

In the refresh operation, not all the stored charges but some of themmay be removed. A voltage that decreases a depletion bias may be appliedto the common electrode bias line 116. In the refresh operation, thevoltage of the lower electrode 161 may be controlled to set a state toeasily remove the charges.

When a MIS sensor is used as the monitor photoelectric conversionelement 102, it may be laid out to be adjacent to the image sensingphotoelectric conversion element 101 in the pixel along the direction inwhich the gate line 120 runs. The transparent electrode 162 c may beconnected to the power supply. The lower electrode 161 may be connectedto the monitor signal processing circuit 154. In this structure,however, a lead interconnection for the transparent electrode 162 c anda lead interconnection for the lower electrode 161 are necessary. Forthis reason, the light-receiving area (opening ratio) of the imagesensing photoelectric conversion element 101 in a pixel having theseinterconnections may be too small.

To the contrary, according to this embodiment having the above-describedarrangement, for a pixel having a lead interconnection, only one leadinterconnection 163 is arranged. Hence, the light-receiving area(opening ratio) of the image sensing photoelectric conversion element101 in this pixel is large. Additionally, in which embodiment, since avoltage is supplied from the common electrode driver circuit 156 to thelower electrode 161 through the common electrode bias line 116, no powersupply is required. For this reason, the circuit can be simplified, asin the fifth embodiment.

As in the fifth embodiment, some pixels may have no image sensingphotoelectric conversion elements 101 and only the monitor photoelectricconversion elements 102 and lead interconnections for the monitorphotoelectric conversion elements 102 in adjacent pixels. In this case,data from the image sensing photoelectric conversion elements 101decreases. The decrease must be compensated by image processing. Thiscompensation can be done by a conventional image processing technique.

Alternatively, only the pixels of one line in each area R2, and forexample, only 1 (row)×20 (columns) pixels or 3 (rows)×1 (column) pixelsin the area R2 may have the monitor photoelectric conversion elements.

A method of manufacturing the radiation image sensing apparatusaccording to this embodiment will be described next. FIGS. 28A to 28Dand 29A to 29D are sectional views showing steps in manufacturing theradiation image sensing apparatus according to this embodiment.

First, as shown in FIG. 28A, an AlNd film 131 serving as a first metallayer and having a thickness of 500 to 4,000 Å is formed on aninsulating substrate 110 by, e.g., sputtering. An Mo film or Ta film maybe formed as the first metal layer. Alternatively, a multilayered filmmay be formed by sequentially forming a plurality of films. Next, theAlNd film 131 is patterned by photolithography using a resist film 132as a mask to form the sensor electrode 111, control electrode 112, gateline 120, and lower electrode 161. Etching of the AlNd film 131 is doneby a wet process using an etchant containing, e.g., nitric acid,phosphoric acid, and acetic acid. After patterning, the resist film 132is removed.

As shown in FIG. 28B, the first insulating film 113 having a thicknessof 1,500 to 4,000 Å, a semiconductor layer 133 having a thickness of2,000 to 15,000 Å, and an ohmic contact layer 134 having a thickness of100 to 1,000 Å are continuously formed by CVD. The semiconductor layer133 becomes the semiconductor layer (photoelectric conversion layer) 114a of the image sensing photoelectric conversion element 101, asemiconductor layer 114 b of the TFT 103, and the semiconductor layer(photoelectric conversion layer) 114 c of the monitor photoelectricconversion element 102. As the first insulating film 113, for example,an SiN film is used.

Then, the semiconductor layer 133 is etched not entirely but partiallyby only 500 to 5,000 Å by photolithography using a resist film 134having an opening on the control electrode 112 of the TFT 103 as a mask.The semiconductor layer 133 is formed as thick as 2,000 to 15,000 Å toincrease the optical absorption efficiency in the image sensingphotoelectric conversion element 101 and monitor photoelectricconversion element 102. In this state, the series resistance between thesource and the drain of the TFT 103 is high. Hence, the process forthinning the semiconductor layer 133 is executed to reduce the ONresistance of the TFT 103. At this time, the semiconductor layer 133 isetched by, e.g., dry etching. As dry etching, plasma etching ispreferably used because a high process accuracy can be obtained whileminimizing damage to the semiconductor layer 133. Chemical dry etchingwhich can also minimize damage to the semiconductor layer 133 may beused. Alternatively, reactive ion etching at a low power (e.g., about0.1 to 0.2 W/cm²) and high pressure (e.g., about 10 to 30 Pa) may beperformed. After patterning, the resist film 134 is removed.

As shown in FIG. 28C, an ohmic contact layer 135 having a thickness of100 to 1,000 Å is formed by CVD. If silicon oxide is present in theinterface between the semiconductor layer 133 and the ohmic contactlayer 135, a preprocess using hydrofluoric acid (e.g., about 0.1 to 10wt %) may be executed. If an organic film is inserted, it may be removedby irradiating it with oxygen plasma. In addition, a final process usinghydrogen plasma may be executed in the CVD apparatus immediately beforeformation of the ohmic contact layer 135.

Next, a through hole 127 is formed by photolithography using a resistfilm 136 as a mask. The through hole 127 electrically connects a drainelectrode 117 d of the TFT 103 to the sensor electrode 111 of the imagesensing photoelectric conversion element 101. Charges generated when thelight-receiving portion absorbs visible light are read, through thedrain electrode 117 d, from the sensor electrode 111 capacitivelycoupled to the light-receiving portion.

To improve the coverage of a metal film to be formed later, chemical dryetching is preferably performed to form a hole having a tapered section.If the coverage of the metal film need not be taken into consideration,the process accuracy may be increased by reactive ion etching.Alternatively, the hole may be formed by plasma etching. Afterpatterning, the resist film 136 is removed.

As shown in FIG. 28D, an ITO film 141 serving as a transparent electrodefilm having a thickness of 100 to 1,000 Å is formed by sputtering. TheITO film 141 is patterned by photolithography using a resist film 142 asa mask to form the transparent electrodes 162 a and 162 c. In thisetching, an organic-acid-based etchant such as oxalic acid that does notdamage the AlNd film 131 exposed to the through hole portion ispreferably used.

When the ohmic contact layers 115 a and 115 c are formed from a filmsuch as a microcrystalline n⁺-film having a low resistivity, the processfrom formation to patterning of the ITO film 141 may be omitted becausethe ohmic contact layers 115 a and 115 c function as the upperelectrode.

As shown in FIG. 29A, an Al film 137 serving as a second metal layer andhaving a thickness of 1,000 to 10,000 Å is formed by, e.g., sputtering.An Mo film or Ta film may be formed as the second metal layer.Alternatively, a multilayered film may be formed by sequentially forminga plurality of films. If an oxide film is formed on the surface of thethrough hole 127, and satisfactory connection to the through hole 127cannot be ensured, a process for removing the oxide film by reversesputtering is inserted before formation of the Al film 137.

The Al film 137 is patterned by photolithography using a resist film 138as a mask to form the common electrode bias line 116. Etching of the Alfilm 137 is done by a wet process using an etchant containing, e.g.,nitric acid, phosphoric acid, and acetic acid. Hence, the Al film 137 isetched slightly inward under the resist film 138. In this patterning,the Al film 137 in regions where the source electrode 117 s, drainelectrode 117 d, and signal line 119 are to be formed is masked by theresist film 138 to prevent etching in this process. After patterning,the resist film 138 is removed.

In this etching process, the transparent electrodes 162 a and 162 c arepreferably crystallized by annealing in advance to prevent any damage tothe transparent electrodes 162 a and 162 c made of the exposed ITO film141.

After the common electrode bias line 116 is formed by patterning, theITO film 141 may be formed and patterned to form the transparentelectrodes 162 a and 162 c. In this case, the transparent electrodes 162a and 162 c are formed to cover the common electrode bias line 116.

After that, as shown in FIG. 29B, the Al film 137 is patterned byphotolithography using a new resist film 139 as a mask to form thesource electrode 117 s, drain electrode 117 d, and signal line 119.Etching of the Al film 137 is done by a wet process using an etchantcontaining, e.g., nitric acid, phosphoric acid, and acetic acid. Hence,the Al film 137 is etched slightly inward under the resist film 139.

At this time, the common electrode bias line 116 that has already beenformed is masked by the resist film 139 to prevent etching in thisprocess. In addition, to prevent the transparent electrode 162 a andohmic contact layer 135 in the opening region of the image sensingphotoelectric conversion element 11 from being removed by dry etching ofthe next process, not only the common electrode bias line 116 but alsothe entire opening region of the image sensing photoelectric conversionelement 101 is masked by the resist film 139.

As shown in FIG. 29B, dry etching is performed using the resist film 139as a mask to remove the gap portions of the TFT 103, i.e., the ohmiccontact layer 135 between the sources and the drains, thereby formingohmic contact layers 115 a to 115 c.

As shown in FIG. 29C, unnecessary portions of the semiconductor layer133 and ohmic contact layer 135 are removed by photolithography using aresist film 140 as a mask to define the opening region of the imagesensing photoelectric conversion element 101 and form the semiconductorlayers 114 a to 114 c. After patterning, the resist film 140 is removed.

The unnecessary portions of the first insulating film 113 are notremoved in this embodiment. However, they may be removed. When the firstinsulating film 113 is left without being removed, the etching processfor removing the unnecessary portions of the semiconductor layer 133 andohmic contact layer 135 is preferably executed by using plasma etchingin order to ensure the process accuracy because the selectivity ratiobetween the semiconductor layer 133 and the SiN film that constitutesthe first insulating film 113 can readily be ensured in plasma etching.

As shown in FIG. 29D, the second insulating film 118 serving as aprotective film and having a thickness of 2,000 to 10,000 Å is formed byCVD. As the second insulating film 118, for example, an SiN film can beformed. In this way, the image sensing photoelectric conversion element101, monitor photoelectric conversion element 102, and TFT 103 can beformed.

A phosphor layer (not shown) is formed. To ensure electrical connection,the protective film at the periphery is removed by patterning and dryetching using photolithography. Thus, a radiation image sensingapparatus can be completed.

In the present invention, the position of the monitor photoelectricconversion element 102 (second semiconductor conversion element) in apixel is not particularly limited. A TFT sensor as in the fifthembodiment may be arranged in the way of this embodiment. Alternatively,a MIS sensor as in this embodiment may be arranged in the way of thefifth embodiment.

According to the fifth and sixth embodiments, the second semiconductorconversion element is formed on the same substrate as that of the firstsemiconductor conversion element. Hence, the entire apparatus can bemade compact and lightweight. In addition, AEC can be executed on thebasis of a radiation dose detected through the second semiconductorconversion element. Since radiation is not attenuated by the secondsemiconductor conversion element, an image having a high image qualitycan be obtained.

The present invention is not limited to each of the first to sixthembodiments. The embodiments may be appropriately combined. For example,in the arrangement (first to fourth embodiments) having an image readsensor formed on the same layer as that of the second conversion element(AEC sensor or radiation monitor sensor), the electrode (theinterconnection connected to the electrode) of the second conversionelement and the control electrode (the interconnection connected to theelectrode) of the switch element may be commonly connected, as describedin the fifth and sixth embodiments. According to this arrangement, theinterconnection structure becomes simpler. In addition, thelight-receiving areas of both of the first conversion element for imagereading and the second conversion element for AEC and/or radiationmonitor can be increased.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. A radiation image sensing apparatus for sensing a radiation by a sensing unit and outputting an electric signal corresponding to the sensed radiation, said sensing unit comprising: an insulating substrate; a conversion section arranged over the insulating substrate and, configured to have a first semiconductor conversion element for converting the radiation into an electrical signal and a switch element connected to the first semiconductor conversion element; a second semiconductor conversion element arranged over the insulating substrate, configured to convert the radiation into an electrical signal for detecting a dose of the radiation incident on said conversion section; and a bias line which is connected to a first electrode arranged for said first semiconductor conversion element and a second electrode arranged for said second semiconductor conversion element, and at least one of the first electrode and the second electrode includes a transparent electrode layer, wherein a first pixel region, which includes the first semiconductor conversion element and the second semiconductor conversion element, and a second pixel region, which includes the first semiconductor conversion element and no second semiconductor conversion element, are arranged on the insulating substrate, the size of the first pixel region is substantially equal to that of the second pixel region, and a light-receiving area of the first semiconductor conversion element in the first pixel region is smaller than that of the first semiconductor conversion element in the second pixel region.
 2. The apparatus according to claim 1, wherein said switch element comprises a thin film transistor.
 3. The apparatus according to claim 1, wherein said second semiconductor conversion element detects the total dose of the radiation.
 4. The apparatus according to claim 2, wherein: said first semiconductor conversion element and said thin film transistor are arranged in a matrix on said substrate, the first electrode is connected to one of a plurality of bias lines arranged in parallel, and the second electrode is connected to the bias line to which the first electrode of said first semiconductor conversion element adjacent to said second semiconductor conversion element is connected.
 5. The apparatus according to claim 1, wherein: said second semiconductor conversion elements comprises a plurality of second semiconductor conversion elements in said conversion section, and when an array of the first and second pixels which are arranged in a direction in which the bias line runs is defined as a row, and an array of the first and second pixels which are arranged in a direction perpendicular to the row is defined as a column, at least some of said plurality of second semiconductor conversion elements are formed in a plurality of second pixels which constitutes the same row or column.
 6. The apparatus according to claim 1, wherein said second semiconductor conversion element has a structure of a field effect transistor which uses the second electrode as one of source and drain electrodes.
 7. The apparatus according to claim 6, wherein at least one electrode selected from the group consisting of the other of the source and drain electrode of said second semiconductor conversion element and a control electrode is connected between a plurality of second pixels.
 8. The apparatus according to claim 1, wherein said second semiconductor conversion element has a MIS structure having the second electrode.
 9. The apparatus according to claim 8, wherein said second semiconductor conversion element has an electrode which sandwiches an insulating film and a semiconductor film with the second electrode and is connected between a plurality of second pixels.
 10. The apparatus according to claim 1, wherein the second electrode has a transparent electrode film which comes into contact with the bias line.
 11. The apparatus according to claim 1, wherein said second semiconductor conversion element has an ohmic contact layer which comes into contact with the bias line as the second electrode.
 12. The apparatus according to claim 1, wherein said first semiconductor conversion element has a MIS structure having the first electrode.
 13. The apparatus according to claim 1, wherein the first electrode has a transparent electrode film which comes into contact with the bias line.
 14. The apparatus according to claim 1, wherein said first semiconductor conversion element has an ohmic contact layer which comes into contact with the bias line as the first electrode. 